Electrical cables with non-metallic jackets and methods of fabricating the same

ABSTRACT

An electrical cable having a plurality of conductors including a grounding conductor and at least one power-carrying conductor. The plurality of conductors disposed approximately in parallel within an outer jacket such that the electrical cable has a substantially elongated horizontal cross-section.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a division of U.S. Non-provisionalapplication Ser. No. 12/284,660, filed Sep. 24, 2008, now abandoned, andclaims the benefit of U.S. Provisional Application Ser. No. 61/002,102,filed Nov. 6, 2007.

FIELD OF INVENTION

The present invention relates in general to electrical cables andmethods of their manufacture, and in particular to electrical cableswith non-metallic jackets and methods of fabricating the same.

BACKGROUND OF INVENTION

Many building applications require electrical cables consisting of threeinsulated conductors and a bare ground conductor, preferably copper, allof which are surrounded by a non-metallic sheath or jacket. UnderwritersLaboratories (UL) Standard 719, for example, defines such cables underthe general designation “NM” for non-metallic sheathed cables, and theparticular designation “NM-B” for building wire with a non-metallicsheath. The NM-B type of electrical cable is widely used in the buildingand construction industry, including for the new construction andremodeling of single-family housing and apartment-type residences.

There are at least two common NM and NM-B cable constructions usingthree insulated conductors and a bare ground. In what is typically knownas a “round” construction, the inner insulated conductors and theassociated bare ground conductor are “cabled” on a machine to produce asingle inner construction in which all of the conductors are twistedtogether with a preferred lay-length and diameter. The bare ground wireis normally wrapped in a paper sheath, as can be the entire innerassembly of the twisted-together insulated and bare conductors. These“tabled” inner conductors are jacketed with a polyvinyl chloride (PVC)resin outer jacket to produce the finished cable.

Cabling gives the inner conductors a uniformly tight, roundedconstruction that holds up well for the final jacketing application. Italso gives the finished cable a uniformly round appearance. Cabled innerconductors also inherently protect against possible movement, loosening,and ensuing damage of the individual conductors as they pass throughcapstans, dies, and paper folders during the various manufacturingphases. However, cabling the inner conductors disadvantageously addslabor-intensity and cost to the manufacturing process in comparison toother methods of construction.

The second typical type of construction of three conductor with bareground NM and NM-B type electrical cables is the “bundled” construction.In the bundled construction, the inner insulated conductors and groundwires are not uniformly cabled. Instead the insulated conductors andbare grounding wires are randomly bundled, and sometimes intermittentlytwisted, in a quasi-rounded, or roughly square or diamond shapedfashion. A helical binder cord may or may not be used prior to thejacketing process. The bare ground wire and the entire innerconstruction are wrapped in paper before jacketing.

Bundling the inner conductors is more cost effective than cabling sincecertain aspects of the cabling process are eliminated duringmanufacture. However, bundling poses a number of other problems. Duringthe jacketing, the individual conductors, which are not tightly cabledby twisting, can intermittently overlap or misalign. Additionally, theindividual inner conductors can unpredictably and non-uniformly move andcompete for space on capstans, in paper folders, or in dies, which candamage, crush, kink, or otherwise compromise the integrity of thecurrent-carrying conductors and ground wires. The bundled innerconductors are also less uniform in appearance and assembly than cabledinner conductors.

Furthermore, the appearance of the outer finished jacket surroundingnon-parallel, randomly bundled inner conductors can in turn benon-uniform and unpredictable. This can create problems duringinstallation, since cables with inconsistently shaped outer jackets aredifficult to pull through, under, or around joists, either alone or inconjunction with other wires. Bundle-constructed cables also createmarketing and quality control problems, since production personnel andend users sometimes mistakenly associate an inconsistent non-uniformouter aesthetic of a finished product with manufacturing defects.

Hence, a need exists for new electrical cables and methods of theirmanufacture that address the foregoing problems with conventional cabledand bundled electrical cables with non-metallic sheaths. In addition toaddressing these problems, such electrical cables and manufacturingmethods should meet the requirements of the relevant NM and NM-B typeelectrical cable standards, particularly those related to electricalcables with three insulated conductors and a bare ground wire.

SUMMARY OF INVENTION

The principles of the present invention are embodied, in one exemplaryembodiment, in an electrical cable having a plurality of conductorsincluding a grounding conductor and at least one power-carryingconductor. The plurality of conductors are disposed approximately inparallel within an outer jacket such that the electrical cable has asubstantially elongated horizontal cross-section.

Generally, the principles of the present invention provide forelectrical cables having finished jacket and overall appearance that areuniform, and non-round. Moreover, by avoiding the cabling step, the costand labor intensity of the manufacturing process are substantiallyreduced. Advantageously, such electrical cables can be constructed usingstandard type pay-offs with reels or stems that supply both insulatedand bare copper conductors to a conventional extruding head receiving asteady supply of jacketing compound.

BRIEF DESCRIPTION OF DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is cross-sectional diagram of a prior art electrical cable with anon-metallic sheath and cabled inner conductors;

FIGS. 2A and 2B are cross-sectional diagrams of prior art electricalcables with non-metallic sheaths and bundled inner conductors,respectively with and without binding cord;

FIGS. 3A and 3B are cross-sectional diagrams of representativenon-metallic sheathed cables embodying the principles of the presentinvention, respectively with and without binding cord;

FIG. 4A is a diagram illustrating a representative process according tothe principles of the present invention for fabricating the electricalcable of FIG. 3A;

FIG. 4B is a diagram illustrating a representative process according tothe principles of the present invention for fabricating the electricalcable of FIG. 3B; and

FIG. 5 is a diagram of an exemplary guide plate suitable or use in theprocesses shown in FIGS. 4A and 4B.

DETAILED DESCRIPTION OF THE INVENTION

The principles of the present invention and their advantages are bestunderstood by referring to the illustrated embodiment depicted in FIGS.1-5 of the drawings, in which like numbers designate like parts.

FIG. 1 is a diagram of a cross-section of a conventional finished three(3) conductor with ground NM or NM-B type electrical cable 100 having around construction with cabled inner conductors. In cable 100, three (3)insulated conductors 101 a, 101 b, and 101 c, preferably of copper, areeach constructed with an insulation layer 102, preferably of polyvinylchloride (PVC) resin and sheathed with a conductor jacket 103,preferably of nylon.

Ground conductor 104 is wrapped in a filler-type sheath 105, preferablypaper, as is the entire internal construction. Surrounding insulatedconductors 101 a, 101 b, and 101 c, ground conductor 104, and fillers105 is a non-metallic jacket 106. All four interior conductors (i.e.insulated conductors 101 a, 101 b, and 101 c, and ground conductor 104)have been “cabled,” which gives a round shape to the profile of cable100.

FIG. 2A depicts a cross-section of a conventional finished three (3)conductor with ground NM or NM-B type electrical cable 200 a in whichthe inner conductors have been bundled in a quasi-rounded, diamond, orsquare stacked formation, with a binder cord.

In cable 200 a, three (3) insulated conductors 201 a, 201 b, and 201 c,preferably of copper, are constructed with an insulation layer,preferably of polyvinyl chloride (PVC) resin 202 and sheathed with aconductor jacket 203, preferably of nylon. Ground conductor 204 iswrapped in a filler-type sheath 205, preferably paper, as is the entirebundle of insulated conductors 201 a, 201 b, and 201 c and groundconductor 204. Surrounding insulated conductors 201 a, 201 b, and 201 c,ground conductor 204 and fillers 205 is non-metallic jacket 206. Allfour (4) interior conductors (e.g. insulated conductors 201 a, 201 b,and 201 c, and ground conductor 204) in cable 200 a are held together bya binding cord 207, which gives cable 200 a a more or less roundedprofile.

FIG. 2B illustrates an alternate conventional bundled cable 200 b, whichis similar to cable 200 a discussed above, except that bundled cable 200b does not utilize a binder cord.

A first illustrative embodiment of the principles of the presentinvention is electrical cable 300 a shown in the cross-sectional diagramof FIG. 3A. Generally, electrical cable 300 a comprises a finished three(3) conductor with ground NM or NM-B type electrical cable with aparallel construction in which the inner conductors are all heldapproximately parallel to each other with a binder cord before theexecution of paper barriers and the overall jacket. The overallhorizontal cross-section of cable 300 a is elongated, providing two (2)generally flat major sidewalls and two (2) generally rounded lateraledges.

Specifically, cable 300 a includes three (3) insulated conductors 301 a,301 b, and 301 c, preferably of copper, each constructed with aninsulation layer 302, preferably of polyvinyl chloride (PVC) resin andsheathed with a conductor jacket 303 preferably of nylon. The groundconductor 304 is wrapped in a filler-type sheath 305, preferably paper,as is the entire construction prior to the final jacket. Surrounding theinsulated conductors 301 a, 301 b, and 301 c, ground conductor 304, andfillers 305 is non metallic jacket 306, preferably of PCV resin. Allfour (4) conductors (i.e. insulated conductors 301 a, 301 b, and 301 cand ground conductor 304) have been laid approximately parallel to eachother and wrapped in a binding cord 307, which gives an oval, parallelprofile to electrical cable 300 a.

FIG. 3B illustrates a second exemplary electrical cable 300 b embodyingthe present inventive principles. Electrical cable 300 b is a finishedthree (3) conductor with ground NM or NM-B type electrical cable with aparallel construction similar to electrical cable 300 a, with theexception that the inner conductors (i.e. insulated conductors 301 a,301 b, and 301 c, and ground conductor 304) have all been placedparallel to each other without a binder cord before the execution ofpaper barriers 305 and overall jacket 306.

An illustrative fabricating system 400 a, according to the principles ofthe present invention and suitable for fabricating electrical cable 300a of FIG. 3A, is shown in FIG. 4A. (The process of fabricatingelectrical cable 300 a is not, however, limited to fabricating system400 a; alternate fabrication systems and methods may be used, asappropriate.)

Fabricating system 400 a includes supply stations or pay-offs 401 a, 401b, and 401 c supplying insulated conductors 301 a, 301 b, and 301 b, andsupply station or pay-off 402 supplying bare ground wire 304. Allconductors pass through various primary stages of alignment by way ofconventional conduits, capstans, or pulleys (not shown) before passingthrough a guide plate 403. Guide plate 403 gives a more exactingalignment of all the conductors 301 a, 301 b, 301 c, and 304, especiallysuch that bare ground conductor 304 alone passes through first paperfolder 404, which surrounds ground conductor 304 with paper (filler)305. An additional paper separator apparatus 405 underneath prevents theground wire paper from becoming entangled with the moving conductors.

After the ground wire 304 has been wrapped in paper, all four conductors301 a, 301 b, 301 c, and 304 pass through a guide plate 406 beforepassing through the center of the cone of binder twine apparatus 407,which helically wraps binder twine 307 around insulated conductors 301a, 301 b, 301 c, and paper covered bare ground wire 304, along theentire length of the construction.

After receiving the binder twine, all conductors 301 a, 301 b, 301 c,and 304 pass through a binder-twine and paper separator apparatus 408before passing through guide plate 409. All conductors 301 a, 301 b, 301c, and 304 then pass through a second paper folder 410, which allows forpaper sheath 305 to be applied and completely surround the entireconstruction. The entire paper-covered construction passes through aparallel-type retainer 411 and parallel-type extrusion tip 412 and die413 at the extruder head, which forms the external jacket 306. A typicalembossing wheel, laser printer, cooling trough, and take-up (not shown)complete the process.

FIG. 4B illustrates a second fabrication system 400 b, suitable formanufacturing electrical cable 300 b, which does not utilize bindingtwine. Fabrication system 400 b is similar to fabrication system 400 b,with the exception that binder twine apparatus 407 and paper separatorapparatus 408 are no longer required (alternate techniques may be used,as appropriate, to construct cable 300 b).

FIG. 5 is a diagram of an exemplary guide plate 500 suitable for use inthe processes shown in FIGS. 4A and 4B as any or all of guide plate 403,guide plate 406, and guide plate 409. Guide plate 500 includes generallyflat metal plate or bracket 501 supporting a removable guide die 502.Guide die 502 includes three (3) slots 503 a-501 b for guiding insulatedconductors provided by payoffs 401 a-401 c and a slot 504 for guidingthe bare grounding conductor provided by payoff 402. (In the illustratedembodiment slots 503 a-503 c overlap to form a single aperture, althoughthis is not a requirement for alternate embodiments.) Guide die 502directs the insulated and bare conductors generally in parallel suchthat the ultimate cable 300 a/300 b can be formed without twisting orcabling.

The embodiments of the principles of the present invention realizesubstantial advantages over the prior art. Among other things, sincecabling is not performed on the inner conductors, the manufacturingprocess is streamlined, thereby increasing efficiency and reducing costsrelative to conventional cabled conductor fabrication techniques.Furthermore, in contrast to conventional bundled electrical cables, thepresent principles provide for more aesthetically uniform electricalcables, which reduces the possibility that non-defective cables will bemistakenly perceived as defective. Functionally, horizontally elongatedelectrical cables according to the inventive principles are easier topull over or through building structures, such as joints, and thesubstantially flat major sidewalls essentially allow for the stacking ofmultiple cables by the end user.

Various modifications of the disclosed embodiments, as well asalternative embodiments of the invention, will become apparent topersons skilled in the art upon reference to the description of theinvention. It should be appreciated by those skilled in the art that theconception and the specific embodiment disclosed might be readilyutilized as a basis for modifying or designing other structures forcarrying out the same purposes of the present invention. It should alsobe realized by those skilled in the art that such equivalentconstructions do not depart from the spirit and scope of the inventionas set forth in the appended claims.

It is therefore contemplated that the claims will cover any suchmodifications or embodiments that fall within the true scope of theinvention.

What is claimed is:
 1. A method of fabricating an electrical cable, theelectrical cable including a plurality of insulated conductors and abare conductor disposed approximately in parallel within an outer jacketsuch that the electrical cable has an elongated horizontalcross-section, comprising: parallelizing the insulated conductors andthe bare conductor by feeding the plurality of insulated conductors andthe bare conductor through at least one guide plate; and extruding theouter jacket over the parallelized insulated and bare conductors suchthat the electrical cable has the elongated horizontal cross-section;wherein parallelizing comprises: passing the insulated conductors andthe bare conductor through a first guide plate; surrounding the bareconductor with a paper sheath; and passing the insulated conductors andthe paper-sheathed bare conductor through a second guide plate.
 2. Themethod of claim 1, further comprising surrounding the parallelizedinsulated and bare conductors with a paper sheath prior to extruding. 3.The method of claim 1, further comprising surrounding the parallelizedinsulated conductors and the bare conductor with binding twine prior toextruding.
 4. A method of fabricating an NM-type electrical cable:passing a plurality of insulated conductors and a bare conductor througha first guide plate to parallelize the plurality of insulated conductorsand the bare conductor; passing the bare conductor through a paperfolder to wrap the bare conductor with paper; passing the insulatedconductors and the paper-wrapped bare conductor through a second guideplate to parallelize the insulated conductors and the paper-wrapped bareconductor; passing the parallelized insulated and paper-wrapped bareconductors through a paper folder to wrap the parallelized insulated andpaper-wrapped bare conductors with paper; and extruding a jacket aroundthe paper-wrapped parallelized insulated and paper-wrapped bareconductors to produce an NM-type cable having a generally elongatedhorizontal cross-section with the insulated and the paper-wrapped bareconductors disposed generally in parallel within the jacket withoutcabling or bundling.
 5. The method of claim 4, further comprising: priorto passing the parallelized insulated and paper-wrapped bare conductorsthrough the paper folder, wrapping a binding cord around theparallelized insulated and paper-wrapped bare conductors.
 6. The methodof claim 5, wherein wrapping a binding cord around the parallelizedinsulated and paper-wrapped bare conductors comprises: passing theparallelized insulated and paper-wrapped bare conductors through abinder twine application stage for helically winding the binder twinearound the parallelized insulated and paper-wrapped bare conductors; andpassing the twine-wrapped parallelized insulated and paper-wrapped bareconductors through a twine-paper separator stage.
 7. The method of claim4, wherein extruding a jacket around the paper-wrapped parallelizedinsulated and paper-wrapped bare conductors comprises: passing thepaper-wrapped parallelized insulated and paper-wrapped bare conductorsthrough a parallel retainer; passing an assembly exiting the parallelretainer through a parallel-type extrusion tip; and passing an assemblyexiting the parallel-type extrusion tip through an extrusion die toproduce the NM-type cable.
 8. The method of claim 4, wherein passing theplurality of insulated conductors and a bare conductor through a firstguide plate comprises passing each of the insulated conductors and thebare conductor through a corresponding one of a plurality of generallyround apertures formed in parallel through a guide plate.
 9. The methodof claim 4, wherein passing the insulated conductors and thepaper-wrapped bare conductor through a second guide plate comprisespassing each of the insulated conductors and the paper-wrapped bareconductor through a corresponding one of a plurality of generally roundapertures formed in parallel through a guide plate.
 10. A method offabricating an NM-type electrical cable: parallelizing three insulatedconductors and a bare conductor; wrapping the bare conductor with paper;parallelizing the three insulated conductors and the paper-wrapped bareconductor; wrapping the parallelized three insulated and paper-wrappedbare conductors with paper to produce a paper-wrapped assembly; andforming a jacket around the paper-wrapped assembly to produce an NM-typecable with a generally elongated horizontal cross-section with the threeinsulated conductors and the paper-wrapped bare conductor disposedgenerally in parallel without bundling or cabling.
 11. The method ofclaim 10 wherein parallelizing the three insulated conductors and thebare conductor comprises passing the three insulated conductors and thebare conductor through a first guide plate.
 12. The method of claim 10wherein wrapping the bare conductor with paper comprises wrapping thebare conductor with a paper folder.
 13. The method of claim 10, whereinparallelizing the three insulated and paper-wrapped bare conductorscomprises passing the three insulated conductors and the paper-wrappedbare conductor through a guide plate.
 14. The method of claim 10,wherein wrapping the parallelized three insulated and paper-wrapped bareconductors with paper to produce a paper-wrapped assembly comprisewrapping the parallelized three insulated and paper-wrapped bareconductors with a paper folder.
 15. The method of claim 10, whereinforming a jacket around the paper-wrapped assembly comprises extrudingplastic around the paper-wrapped assembly.
 16. The method of claim 10,further comprising wrapping binding cord around the parallelized threeinsulated conductor and paper-wrapped bare conductors prior to wrappingthe parallelized three insulated and paper-wrapped bare conductors withpaper to produce the paper-wrapped assembly.